A remote sensing system uses a detector to sense the reflected or emitted energy from the earth's surface, perhaps modified by the intervening atmosphere. The sensor can be on a satellite, aircraft, or drone. The sensor turns the energy into a voltage, which an analog to digital converter turns into a single integer value (called the Digital Number, or DN) for the energy. Alternatively a digital detector can store the DN directly. We can then display this value with an appropriate color to build up an image of the region sensed by the system. The DN represents the energy sensed by the sensor in a particular part of the electromagnetic spectrum, emitted or reflected from a particular region. The principles can also be applied to sonar imagery, especially useful in water where sound penetrates readily whereas electromagnetic energy attenuates rapidly.
Remote sensing systems can be active or passive: active systems put out their own source of energy (a large "flash bulb") whereas passive systems use solar energy reflected from the surface or thermal energy emitted by the surface. Active systems can achieve higher resolution.
Satellite resolution considers four things: spatial, spectral, radiometric, and temporal resolution.
Electromagnetic radiation and the atmosphere control many aspects of a remote sensing system.
Satellite orbits determine many characteristics of the imagery, what the satellite sees, and how often it revisits an area.
The signal to noise ratio is important for the design of remote sensing systems.
Satellite band tradeoffs.
Interpreting satellite reflectance patterns and images uses various statistical measures to assess surface properties in the image.
The colors used on the display are gray shading for single bands, and RGB for multi-band composites. We can also perform image merge and sharpening to combine the advantages of both panchromatic (higher spatial resolution) and color imagery (better differentiation of surface materials).
Keys for image analysis
Spectral reflectance library--different materials reflect radiation differentlyRemote Sensing Options in MICRODEM
Last revision 5/19/2020